Injection mold wherein moveable cavity portions act to close the mold gates and further compress the mold material

ABSTRACT

A method of molding and a mold are provided for encapsulating devices such as axial lead cylindrical electrical devices in which two separable portions of the mold closely embrace the axial leads near the axial ends of the mold cavity and one of the mold portions includes piston-like parts, one for each molding cavity, which moves between at least two positions. In one position of a piston-like part of the mold, and mold cavity is open to receive encapsulating fluid and in the other position of the part the mold cavity is completely closed. In a modification, the piston-like parts are each shaped and positioned to form parts of adjacent molding cavities. The molding process involves supplying encapsulating fluid to the several cavities by applying pressure to the whole body of fluid and applying higher pressure to the fluid in each molding cavity.

United States Patent Spanjer [451 Aug. 22, 1972 54] INJECTION MOLDWHEREIN 2,380,084 10/1945 Strauss 1 8/16 F MOVEABLE CAVITY PORTIONS ACT2,913,767 11/1959 Simon 18/30 WR TO CLOSE THE MOLD GATES AND 3,268,9608/196 Morton ..18/3O WR Inventor:

FURTHER COMPRESS THE MOLD MATERIAL Keith Gordon Spaniel, Scottsdale,Ariz.

Assignee: Motorola, Inc., Franklin Park, Ill.

Filed: Nov. 19, 1969 Appl. No.: 878,104

425/250, 425/443 Int. Cl ..B29c 1/00 Field of Search..l8/3O PT, 30 WC,36, DIG. l0,

I8/DIG. 38, I D, 2 RM, 2 RP, 2TP, 16 F, 42'. D, 5 E, 42 J, 30 WM, 30 WR,30 PM;

References Cited UNITED STATES PATENTS 9/1970 Burns ..249/97 X PrimaryExaminer l. Spencer Overholser Assistant Examiner-David S. SafranAttorney Mueller and Aichele ABSTRACT A method of molding and a mold areprovided for encapsulating devices such as axial lead cylindricalelectrical devices in which two separable portions of the mold closelyembrace the axial leads near the axial ends of the moldcavity and oneofthe mold portions includes piston-like'parts, one for each moldingcavity,

3 Claims, 8 Drawing figures PATENTEDnuszz I972 SHEET 2 [IF 3 Q2 @Q mKeith Gordon Spanjer m wd MA ATTY'S.

PATENTEDwszz 1972 3,685,784

saw a or 3 Fig. 8

I INVENTOR.

Keith Gordon Spanjer BY M M 9* ATTY'S.

INJECTION MOLD WHEREIN MOVEABLE CAVITY PORTIONS ACT TO CLOSE THE MOLDGATES AND FURTHER COMPRESS THE MOLD MATERIAL BACKGROUND In the prior artmethod of encapsulating a device, two mold portions are provided which,when put together in a proper manner, form a molding cavity. The articleto be encapsulated is placed in the cavity and encapsulatingfluid is fedunder pressure into the cavity by way of the small passageway called agate in either one of the portions of the mold or partly in bothportions of the mold. A connecting tube or runner is provided connectingthe central container for the molding fluid to the several gates. Sincethe gate area is small in comparison to the cross-sectional area of thecavity, the velocity of flow of encapsulating fluid is high, whereby thedevice to be encapsulated may be damaged by the flow. The fluid hardensand the mold parts are separated and the encapsulated item is taken outof the mold, usually by hand. The gate material as well as the materialin the runner is wasted. Also, the gate material must be broken off thecapsule leaving a rough spot that may interfere with labelling thecapsule, especially if the capsule is small, whereby it may be necessaryto smooth the surface of the article before it can be sold. Furthermore,if the capsule has axial leads, the encapsulating material may contactthe leads for an undesirable distance along the length thereof, wherebythe material must be cleaned off of the leads. Such cleaning andsmoothing operations are difficult and expensive. In addition, in theprior art,'since pressure is applied to the molding liquid at a distancefrom the mold cavity, the mold cavity may not be full, or, if full, allparts of the molding material may not have the same pressure appliedthereto. Therefore, the molded articles as provided by the prior artmethod and mold may have differing densities in different portionsthereof.

It is an object of this invention to provide an improved method ofmolding.

It is an object of this invention to provide an improved mold.

It is another object of this invention to provide a method of moldingand a molding apparatus in which the amount of waste of molding materialis minimized, the molding material is kept off the leads to thecompleted capsule, and closeable gate is provided, and the density ofthe molding material of the encapsulated package is unifonn throughoutthe volume thereof.

SUMMARY In accordance with the method of this invention, theencapsulating fluid is fed to molding cavities through large gates,which can be opened and closed, under centralized pressure, and as thegate is closed localized pressure is applied to the fluid in eachcavity. When the fluid has hardened, the capsule is ejected from thecavity. Further in accordance with this invention, a mold is providedhaving an upper and a lower portion, which when fitted together providea cavity of the shape of the finished encapsulated article or capsule.The lower portion includes at least one piston-like part for each cavitywhich is moveable with respect to the lower portion. When a piston is inone of its extreme positions, a

passageway is provided along the length of the mold are formed in themold portions with encapsulating fluid. The passageway is so large thatthe flow of fluid into the cavities is slow, whereby the article to beencapsulated is not damaged by fluid flow. When the piston is in anintermediate position, the cavity takes the shape of the finishedcapsule and the feeding gate is cut ofi.

In the process of moving the piston to its intermediate position, theencapsulating fluid is compressed into the mold cavity, whereby thedensity of the capsule is made-uniform. Since the feed gate is cut offwhen the piston arrives at its intermediate position, there is no gatematerial whereby waste of encapsulating material is reduced and thesurface of the capsule is smooth. The fluid is fed from cavity to cavityalong the length of the mold whereby the passageway for the fluid isshortened, further saving encapsulating fluid. If the capsule has leads,the upper and lower portions of the mold are tightly clamped on theleads at the ends of the cavity before the fluid is forced into thecavity, whereby no or very little encapsulating fluid comes into contactwith the leads, whereby cleaning the leads is avoided. After the fluidis hardened, the piston is moved to its other extreme or to an ejectingposition to eject the finished The invention will be better understoodupon reading the following description in connection with theaccompanying drawing in which:

FIG. 1 is an exploded vertical section of a mold according to thisinvention for providing a cylindrical capsule having axial leads andshowing the relative position of the mold portions and the finishedcapsule,

FIG. 2 is an exploded vertical section of the mold of FIG. 1 taken,however, at from the section of- FIG. 1, and also showing the relativeposition of the mold portions to the finished capsule,

FIG. 3 is a top view of the lower portion of the mold of FIGS. 1 and 2,

FIGS. 4 and 5 are sectional views of the mold portions that are usefulin explaining the inventive method and the operation of the mold ofFIGS. 1-3,

FIGS.'6 and 7 are, respectively, vertical section and a plan view of amodified mold of this invention, and

FIG. 8 is a top view of a molding machine using the described molds andshowing how the encapsulating fluid is fed to the mold cavity.

In general, in accordance with the prior art, encapsulating material isbought in a granular form; a certain amount thereof is weighed out andheated until it becomes a pliable mass which is called a pill. Thepill'is put into a reservoir such as reservoir 10 of FIG. 8. Thearticles 15 to be encapsulated are placed in the mold cavities in thelower half of the molds and the upper half of the molds is put over thearticle, and the two halves of the molds are fixed together. To assistin feeding the molding machine of FIG. 8, the supports 9 are loaded witharticles 15, whereby a great many articles 15 may be placed inrespective molding cavities of the lower half of the molds 13 at thesame time. The pill is melted and the fluid is put under pressure ofabout I 3. 3000 pounds per square inch by piston means 11 contained inthe reservoir 10. The fluid runs along passageways 12,12 to the molds13. Centralized pressure is applied by pressure means 11 in the centralreservoir to theliquid, and passageways, not shown JinFIG. 8, areprovided along the molds and individual gates are provided between thepassageways and the in- FIG. 8,four molds 13, each comprising aplurality such as 50 molding cavities, may be supplied with the articlesto be encapsulated and with encapsulation fluid at the same time,whereby about 200 encapsulated articles are made at one time. When it isjudged that all the molds are full, the fluid isallowed to cool down andwhatever material is'left in the reservoir 10, called the cull, and thematerialin the passageway or runners 12 dividual cavities formed by themolds. As is shown in centrally formed with a semi-cylindrical cavity 42that in the passageways extending along the length of v the individualmolds'and the gates (not shown) are thrown away. The molds are takenapart'to take out .20 manually the finished articles that have the gatematerial attachedthereto and the gate material ,is broken off and thearticles are polished if necessary. If the article has leads, often theleads have molding material stuck i thereto sofar beyond the end of thecapsule as torequire cleaning the leads. Frequently, the cavities in themolds that are at extreme distance from the reservoir 10 or those'cavitiesfto which the passageway ,or the gate holes has not beencarefully cleaned out are not filled with encapsulating fluid, wherebythe encapsulation of. the article l5v is not perfect. The pressure inencapsulate articles having axial leads. The articles 15 (shown-in FIG.8) .to be encapsulated may include a central rectifying junction andcoaxial leads 18. The finished articles 14, shown in. FIGS. 1 and2,-have a cylindrical "body portion 16 fully encapsulating therectifying junction and axial leads 18 extending from the body portion16.

First, considering FIGS. 1, 2, and 3, the upper portion 20 of a moldembodying the structural aspects of the invention and with which themethod of this invention can be practiced has a semi-cylindrical cavity22 which fits one-half of the circular surface and one-half of each endsurface of the cylinder 16. The groove portions 24,24 of the uppermoldportion are adjacent the semi-eylindrical portion 22 thereof and fitthe upper halfof the leads 18 for a short portion of their length.

Longitudinal grooves 26 are provided in the lower face of the moldportion 20 beyond the lead fitting grooves 2410 provide clearance forleakage of encapsulating fluid-( if any) out of the cavity 22 along theleads l8. Portions 28 of the upper lead portion 20 and beyond thegrooves 26 push the leads 18 down in the comb'part 30" of thelowerportion 32 of the. mold as will be described.

I The lower portion of the mold of FIGS. 1, 2, and 3 in- I cludes theouter comb part30 having lower semi-cylindrical grooves 34 for receivingthe lower part of the leads 18. Longitudinal grooves 36 which match withgrooves 26 are next in the inwardly direction from the combs 30. Grooves38 are provided tofit the lower part of the leads 18 adjacent the cavityfor forming the cylindrical portion 16 of the article 14. As will bemade more clear, when the upper portion 20 and thelower portion 32 abuteach other, the portions 24 and 38 so closely fit the leads 18,18 thatfluid does not leak out, or very little fluid leaks out, along' theleads 18,18.

The bottom of the lower mold portion 32 is provided I with a verticallymoveable piston-like part or slider 40. The top of the piston'40, asshown in FIGS. 2 and 3, is

fits the lower portion of the cylinder 16. The top of the piston 40, onboth sides. of the cavity 42, is flat, as

shown at 44, FIGS. 2. The'center of the lower portion 32 of the moldbetween the sides, of the .pistons40 forrns'flat surfaces 46 which arebelow, by about twenty thousandths of aninch, the-upper orlongitudinally-extending spaced parallel surfaces 48 which extendbetween the grooves on each side of the cavity The piston 40 is moveablebetween its lowest position as shown inFIGS. 2 and 4 in which thesurfaces44 are 1 flush with the surfaces'46 and its intermediateposition shown in FIG. 5.in which the surfaces 44 are flush with thesurfaces 48 and are in tight contact with the surface Q '50 of the uppermold'portion20. When the surface 44 is flush with the surface 46, andwhen the mold portions 20 and 32 are clamped together, leads such as theleads 18 are tightly clamped in'semi-cylindrical grooves 24 I and 38which together'closely embrace the leads 18', the surfaces 48 closelyembrace the leads 18, and the surfaces 48 closely contact thecorresponding portions of the surface of the mold portion 20 between thecavities 22. However, there is a large space I or passageway 99 (seeFIG. 4) between the surface 46 and the corresponding portion of thesurface 50 and also between the upper surface 44 and the correspondingportion of the the surface 50 for flow of fluid from one end of themold, comprising the two mold portions 20 and 32, to the other endthereof. This is shown inFIG. 4 in which the passageway 99 isprovidedalong the whole length of the mold between the surface 50 and. thecavity22 of the upper mold portion 20and the intermediate surface 46 ofthe bottom mold portion 32 '1 and the upper surface 44 and uppercavitysurface 42 of the pistons 44. However, the surface48 of the lowerand the surface 50 of the upper portion 20, including portion 42,including the semi-cylindrical portions 38,

the semi-cylindrical portion 24, contact each other at each end ofcavity portions 22 and 42 or they embrace the leads-l8, whereby fluidscan come in through the passageway 99 as described but cannot leak out.The

passageway 99 -is as wide as the cylindrical cavity 22 and 42 is longand is about twenty thousandths of an inch deep. Thearea of thepassageway is made'large, about 20 percent of the cross-sectional areaof the finished article 14, whereby flow of fluid into the than if asmall gate of several molding cavities is slower the prior art wereused.

In the use of the mold of this invention, the lower j portion 32 of themold with the pistons 40 in their lower position (and with the upperportion of .themold 20 out of theway) is loaded in a known manner withrectifiers 15 (for example) to be encapsulated. Then the upper portion20 of the mold is properly placed on the lower portion 32 and these twoportions 20 and 32 are clamped together in a known manner, the pistons40 being in their lower position. Then encapsulating fluid from thereservoir is fed to the passageway 99 of the completed mold, the fluidrunning in a direction of the arrows 100 in FIG. 8 into and throughsuccessive cavities. When, due to the pressure in the pot 10 as providedby the pressure providing means 11, all the cavities formed by the moldportions and 32 are filled, the cam means 60 is moved in such adirection, to the right as viewed in FIGS. 4 and 5, as to raise all thepistons 40 simultaneously until they take the position shown in FIG. 5in which the top surface 44 of each piston 40 is flush with and contactsthe surface 50 of the upper mold portion 20. The passageway 99 istending surfaces 48 which abut the surface 50 of the upper mold portionlongitudinally and at each side of the cavities that are formed by theupper cavity portions 22 and the lower cavity portions, to be described.

The lower mold portion 100 is formed with fixed bridge portions 102 thatare in central registry with the cavity portions 22 when the moldportions 20 and 100 are properly assembled. The tops of the fixedportions 102 have partly cylindrical cavities 104 formed therein, thecavities 104 forming part of the same cylindrical cavity that fits thecylindrical portion 16 of article 14 of FIG. 1. A piston 106 is providedbetween each two greatly reduced in length because several portionsthereof are cut off between the several pistons 40. The semi-cylindricalsurfaces 42 and 22 form cylindrical cavities which are concentric withthe leads, 18,18 which are embraced by the semi-cylindrical grooves 24and 38. While the cam 60 is pushing the sides 40 upwards, as viewed inFIG. 5, the fluid in the passageway 99 is compressed locally, that is,within each mold cavity comprising the semi-cylindrical portions 22 and42 and to a higher pressure than the compression supplied by the centralcompression means 11 in the cylinder 10. This final higher compressioninsures that the molding cavities are filled and that the compression ineach molding cavity is the same as that in other cavities and also thatthe compression in each cavity is the same art molding machines. Sincethere is no gate hold, the

gate material is not wasted and the gate material need not be brokenofi' the finished article and the surface at the break need not be madesmooth. Also, since the portions at 24 and 38 tightly embrace the leadlines 18 throughout the filling, compressing, and hardening process, nofluid leaks out of the mold along the leads 18, whereby more fluid issaved and whereby the leads need not be cleaned. A greatly improvedproduct, at a greater yield, results from the use of the disclosed molds20 and 32.

When the top portion 20 of the mold is removed, further movement of thecam 60 to the right ejects the finished encapsulated articles, wherebythe pistons 40 not only serve as the lower halves of molding cavitiesand as parts of open and closeable gates, but also as ejectors.

FIGS. 6 and 7 show another mold in accordance with this invention. InFIGS. 17, similar reference characters have been applied to similarparts. The upper mold portion 20 of FIGS. 1-5 and of FIGS. 6 and 7 aresimilar. The lower mold portion 100 differs in a manner to be explained.

As shown in FIG. 7, the lower mold portion includes the combs 30, thelongitudinal grooves 36, the lead embracing grooves 38, and the raisedflat parallelly ex- I fixed portions 102. The top 108 of the pistons 106is flat and when thejpistons 102 are in their intermediate positions,the flat portions 108 tightly fit against the surface 50 of the uppermold portions 20. At each side of the top portions 108, the pistons 106are shaped so that in the intermediate positions of the pistons 106they, with the cavity portions 22 and 104, form a cylindrical cavity ofthe shape of the cylindrical portions 16 of the finished article 14. Inthe lowest positions of the pistons 106 as shown in FIG. 6, a largepassageway 99 is provided for fluid flow along the length of the moldcomprising the mold portions 20 and 100 into a first molding cavity,then into a second, and so on to the last cavity. In the top position ofthe pistons 106, the finished article is ejected from the .open mold.This mold 6f FIGS. 6 and 7 has all the advantages of the mold of FIGS.1-5. In addition, in the mold of FIGS. 6 and 7, many more cavities maybe provided along the length of the mold due to the fact that eachpiston 106 becomes part of two adjacent cavities whereby the gatedistance, the width (as shown in FIGS. 6 and 7) of the flat portion 108,is greatly reduced over the gate distance of FIGS. 105. The pistons 106are moved up by a cam means such as cam 60 of FIGS. 4 and 5.

- Each time an article is molded by the molds of FIGS. 1-7, the moldingfluid is fed into and through the successive molding cavities, wherebythe length of passageways for the fluid is minimized, under pressurethrough wide open gates, whereby the flow of fluid is slow causing nodamage to the device to be encapsulated. Then higher pressure is appliedto the fluid in the cavities as the pistons 40 in FIGS. 1-5 and 106 ofFIGS. 6 and 7 are raised to their intermediate, positions andsimultaneously the gates are closed, whereby the passageway is madestill shorter and whereby no gate material need be broken off the moldedarticle and whereby the density of the molded article is increased andis made uniform from article to'article and from one portion to anotherportion of the molded article. Then, after the fluid has hardened andthe upper portion 20 of the mold is removed, the pistons 40 and 106 areraised still further, whereby the finished articles are ejected. v Ifdesired, an article without leads may be molded. In such case, thesurfaces 48 and 50 will be extended flat without grooves 38 and 24therein; however, the complementary cavities, which may be given anyshape desired, will be retained. Otherwise, no change will be made inthe described molds of the several Figures.

What is claimed is: 1. A mold comprising an upper mold portion having acavity of the shape of a portion of an article to be molded and a flatsurface,

. 7 a lower mold portion having spaced parallelly extending flatsurfaces adapted to contact said flat surface of said upper moldsurface,

said lower mold portions also including spaced fixed bridge poru'ons, I

fixed portions and between said parallel flat surpiston-like moveableparts-positioned between said faces and moveable in directionsperpendicular to I said parallelly extending flat surfaces,

said piston-likepart being shaped to fit another por- Q .tionof anarticle to be molded and an end of said a piston-like portion having aflat'surface adapted to contact said flatsurfaceof said upper moldportions, i said iflat surface positions being spaced from said flatsurface of of said piston-like in one of its said uppermold portion forproviding a passage for molding fluid into said 'c'avityand in 'anotherposition thereof beingin contact with said flat sur-- face of said uppermold portion for preventing passage of fluid to and from said cavity,

said shaped portionof said piston-likepart insaid other positionforminga continuation of the'surface of a molding cavity, and

' said bridge portions'each being shaped to fit an article and (in saidpiston-like portion being shaped to fit two articles, one on eachside ofsaid flat end portions. 2. A mold comprising 7 an upper mold portionhaving a cavity of the shape of a portion of an article to be molded anda flat surface,

a lower mold portion having spaced parallel 1y ex-.

tending flat surfaces adapted to contact said flat surface of said uppermold surface, said lower mold portions also including spaced fixedbridge portions, I piston-like moveable parts positioned between saidfixed portions and between said parallel flat surfaces and moveable indirections perpendicular to said upper moldjportion for providing apassage for molding-fluid into said cavity and in another positionthereof being in contact with said flat surface of said upper moldportion for preventing passage of fluid to and from said cavity,

said shaped portion of said piston-like part in said other positionforming a continuation of surface of a molding cavity, r the ends ofsaid fixed portiom being flat a'nd'lower than said spaced parallelflatsurfaces,

an: end of said moveable piston like part having a cavity therein of theshape of another portion of v the article to'be molded and a flatsurface which is parallel with said lower flat surfaces, and

the flat surface of said piston-like part szasa ossaas gaszc' sa s?molding fluid.

3. Thein'vention of claim 1 in which said cavities are I eachsemi-cylindrical and in which said parallelly extending surfaces ofsaid'lower portion extend perpendicular to the axis ofsaid'semi-cylindrical cavities. I

' a s a a r a of said piston-like in one of its being ma a in oneposition 'thereofto contact the surface of said upper portion and inanother position-thereof 1

1. A mold comprising an upper mold portion having a cavity of the shapeof a portion of an article to be molded and a flat surface, a lower moldportion having spaced parallelly extending flat surfaces adapted tocontact said flat surface of said upper mold surface, said lower moldportions also including spaced fixed bridge portions, piston-likemoveable parts positioned between said fixed portions and between saidparallel flat surfaces and moveable in directions perpendicular to saidparallelly extending flat surfaces, said piston-like part being shapedto fit another portion of an article to be molded and an end of saidpiston-like portion having a flat surface adapted to contact said flatsurface of said upper mold portions, said flat surface of saidpiston-like part in one of its positions being spaced from said flatsurface of said upper mold portion for providing a passage for moldingfluid into said cavity and in another position thereof being in contactwith said flat surface of said upper mold portion for preventing passageof fluid to and from said cavity, said shaped portion of saidpiston-like part in said other position forming a continuation of thesurface of a molding cavity, and said bridge portions each being shapedto fit an article and said piston-like portion being shaped to fit twoarticles, one on each side of said flat end portions.
 2. A moldcomprising an upper mold portion having a cavity of the shape of aportion of an article to be molded and a flat surface, a lower moldportion having spaced parallelly extending flat surfaces adapted tocontact said flat surface of said upper mold surface, said lower moldportions also including spaced fixed bridge portions, piston-likemoveable parts positioned between said fixed portions and between saidparallel flat surfaces and moveable in directions perpendicular to saidparallelly extending flat surfaces, said piston-like part being shapedto fit another portion of an article to be molded and an end of saidpiston-like portion having a flat surface adapted to contact said flatsurface of said upper mold portions, said flat surface of saidpiston-like part in one of its positions being spaced from said flatsurface of said upper mold portion for providing a passage for moldingfluid into said cavity and in another position thereof being in contactwith said flat surfaCe of said upper mold portion for preventing passageof fluid to and from said cavity, said shaped portion of saidpiston-like part in said other position forming a continuation of thesurface of a molding cavity, the ends of said fixed portions being flatand lower than said spaced parallel flat surfaces, an end of saidmoveable piston-like part having a cavity therein of the shape ofanother portion of the article to be molded and a flat surface which isparallel with said lower flat surfaces, and the flat surface of saidpiston-like part being adapted in one position thereof to contact thesurface of said upper portion and in another position thereof to formwith said surface of said upper portion and the surface of said fixedportions a passageway for molding fluid.
 3. The invention of claim 1 inwhich said cavities are each semi-cylindrical and in which saidparallelly extending surfaces of said lower portion extend perpendicularto the axis of said semi-cylindrical cavities.